In recent years, laser surgery has become an important tool for ophthalmic surgeons. The technique involves observation of the patient's eye under considerable magnification by means of a conventional slit lamp while focusing a low power visible laser beam at a desired point in the patient's eye. When the visible beam has been appropriately focused, a high-powered therapeutic beam, outside the visible spectrum but coaxial with the visible beam, is momentarily activated to cut or coagulate the tissue at the spot where the visible beam had been focused.
In the prior art (exemplified by U.S. Pat. No. 3,703,176 to Vassiliadis et al), a laser beam was produced by a laser positioned on a stationary support and connected to the slit lamp by a pair of articulated arms which allowed the slit lamp assembly to be moved into proper focus with respect to the patient's eye. In this arrangement, the laser beam used an optical path movable conjointly with the path of the light slit produced by the illuminator or light source of the slit lamp. As a practical matter, the illuminator needs to be movable with respect to the microscope of the slit lamp, through which the physician observes the eye, to permit observation of the illuminated eye from different directions. As a result, the prior art device not only failed to allow the physician to move the laser beam totally independently of the illumination column, but it also produced an annoying parallax when the microscope was not exactly aligned with the light slit beam. Inasmuch as it is often necessary for the physicial to direct the light slit beam at an angle to his line of vision for better observation, the movement of the laser beam conjointly with the light slit beam created a significant problem.
In addition, the articulated arms fo the prior art required a substantial number of reflections of the laser beams by a series of mirrors. Inasmuch as this is cumbersome and makes it difficult to maintain the instrument in alignment, the use of the articulated arms considerably reduced the ease of use of the lasers.